This research proposal is directed toward an understanding of how the neuregulins (NRGs) affect the proliferation and differentiation of olidendroglial progenitors, their lineages and Schwann cells. The first described neuregulin, NRG-1, is a potent Schwann cell mitogen and appears to have similar effects on oligodendroglial precursors. The ErbB subfamily of receptor protein-tyrosine kinases transduce neuregulin signals. This application proposes to test the hypothesis that the recently identified neuregulin-like molecule, NRG-2, also shares these activities. Specifically, first the sites of NRG-2 will be characterized in the developing rat nervous system in aim 1. In aim 2, the ability of NRG-2 to promote oligodendroglial precursor and schwann cell proliferation will be assessed. Lastly, in aim 3, the specific ErbB receptors activated in these cells will be determined. Through these efforts, we hope to improve our understanding of whether NRG-1 and NRG-2 serve similar or distinct roles in the mammalian nervous system.